Defect generation limits device lifetime and enhances its variability. Previous works mainly addressed the generation kinetics and process. The current understanding is that the microstructure responsible for defect can exist either as a precursor or as a charged defect. A precursor is converted into a defect during stresses, but a defect can return to its precursor status through recovery and/or anneal. This letter will introduce a new concept: defect loss. A lost defect will not return to the precursor status. When stressed again, the lost defect will not reappear. It is found that the defect loss is thermally activated and a reduction of the “permanent component” makes substantial contribution to the loss. This letter opens the way for improving device lifetime through maximizing defect loss.